Rechargeable battery unit and charging method

Abstract

A rechargeable battery unit and method for charging a battery is provided. The battery unit can be connected to a constant current charging device for charging the battery unit. The constant current charging device has a plurality of poles and a cut-off voltage. The battery unit has an internal resistance, a lithium battery cell having a predetermined end-of-charge voltage, and a switch unit. The switch unit is configured to enable alteration of the internal resistance when the predetermined end-of-charge voltage has been reached, such that the voltage at the poles of the constant current charging device is greater than the cut-off voltage of the constant current charging device to terminate the charging process.

The invention claimed is: 
     
       1. A battery unit that can be connected to a constant current charging device for charging the battery unit, the constant current charging device having a plurality of poles and a cut-off voltage, comprising:
 an internal resistance; 
 at least one lithium battery cell having a predetermined end-of-charge voltage; and 
 at least one switch unit, wherein the at least one switch unit is configured to increase the internal resistance when the predetermined end-of-charge voltage has been reached, such that the voltage at the poles of the constant current charging device is greater than the cut-off voltage of the constant current charging device to terminate the charging process. 
 
     
     
       2. The battery unit as claimed in  claim 1 , wherein the switch unit is configured such that the internal resistance is increased depending on the charging voltage of the at least one lithium battery cell. 
     
     
       3. The battery unit as claimed in  claim 1 , wherein the switch unit comprises a controller and a controllable switch element coupled to the controller, wherein the controllable switch element is configured to increase the internal resistance, wherein the controller controls the controllable switch element. 
     
     
       4. The battery unit as claimed in  claim 3 , wherein the controllable switch element comprises at least one electronic component that is selected from the group consisting of ohmic resistors and semiconductor components with modifiable or controllable impedance. 
     
     
       5. The battery unit as claimed in  claim 4 , wherein the controllable switch element or the switch unit comprises a switch, by means of which the at least one electronic component and lithium battery cell can be connected in series to alter the internal resistance. 
     
     
       6. The battery unit as claimed in  claim 3 , wherein the controller controls the switch element based on the charging voltage of the at least one lithium battery cell. 
     
     
       7. The battery unit as claimed in  claim 5 , wherein said switch comprises at least one of an electromechanical switch and an electronic switch. 
     
     
       8. The battery unit as claimed in  claim 7 , wherein said electronic switch comprises a semiconductor switch. 
     
     
       9. The battery unit as claimed in  claim 4 , wherein said semiconductor component comprises a MOSFET transistor. 
     
     
       10. A charging method for charging a battery unit comprising at least one lithium battery cell having a predetermined end-of-charge voltage, wherein the battery unit has an internal resistance and can be connected to a constant current charging device for charging the battery unit, the constant current charging device having a plurality of poles and a cut-off voltage, the method comprising:
 using a switch unit of the battery unit to increase the internal resistance when the predetermined end-of-charge voltage has been reached, such that the voltage at the poles of the constant current charging device is greater than the cut-off voltage of the constant current charging device to terminate the charging process. 
 
     
     
       11. The method as claimed in  claim 10 , wherein the internal resistance is increased by connecting the at least one lithium battery cell in series with an electronic component having a predetermined impedance, or by increasing the predetermined impedance of the electronic component connected in series with the at least one lithium battery cell. 
     
     
       12. The method as claimed in  claim 11 , wherein the component is selected from the group consisting of ohmic resistors and semiconductor components with modifiable or controllable impedance. 
     
     
       13. The method as claimed in  claim 11 , wherein the series connection of the electronic component and the at least one lithium battery cell can be made or canceled using at least one of an electromechanical switch and an electronic switch. 
     
     
       14. The method as claimed in  claim 10 , wherein the internal resistance of the battery unit is decreased when the at least one lithium battery cell falls below a predetermined charging voltage. 
     
     
       15. The method as claimed in  claim 12 , wherein said semiconductor component comprises a MOSFET transistor. 
     
     
       16. The method as claimed in  claim 13 , wherein said at least one of the electromechanical switch and the electronic switch is a controllable switch.